1. Field of the Invention
The present invention relates to a method of fabricating semiconductor devices, and more particularly, to a method of fabricating a phase shift mask.
2. Description of the Related Art
A general blank mask is formed by forming a chrome layer as a transmission preventing film on a quartz substrate and coating a photosensitive film on the resultant structure. A phase shift mask (PSM) is effective in improving resolution and the depth of focus in a process for forming a contact hole.
A halftone PSM generates a sidelobe effect. Accordingly, a photosensitive film in an undesired region is damaged. Thus, if such a problem is not solved, the application field of the halftone PSM becomes narrow.
The sidelobe effect becomes more severe as a pitch between devices becomes narrower due to increasing integration of semiconductor devices. To solve this problem, a halftone rim PSM also uses a rim-type structure used by a quartz PSM.
A conventional rim-type PSM and a fabrication method thereof will now be described in brief referring to the attached drawings.
Referring to FIG. 1, in the conventional rim-type PSM, a plurality of grooves 12, which will become phase shift regions, are formed at regular intervals in a quartz substrate 10. Light shield film patterns 14 are formed on the quartz substrate 10 between the grooves 12, and a rim region 14a is formed between the light shield pattern 14 and the groove 12.
Referring to FIG. 2, in a conventional rim-type halftone PSM, phase shift layer patterns 16 are formed on a quartz substrate 10, between phase non-shift regions 17. Light shield film patterns 18 are formed on the phase shift layer patterns 16. A rim region 18a is formed between the light shield film pattern 18 and the phase shift layer pattern 16.
A method of fabricating the conventional rim PSM shown in FIG. 1 will now be described.
Referring to FIG. 3, a light shield film (not shown) is formed on the quartz substrate 10. A photosensitive film pattern 22 for exposing a predetermined region of the light shield film is formed on the light shield film. An exposed portion of the light shield film is removed using the photosensitive pattern as a mask, thereby forming a light shield film pattern 20 for exposing a predetermined region of the substrate in which phase shifting occurs. Then, the photosensitive film pattern 22 is removed. Consequently, as shown in FIG. 4, a groove 24 is formed to a depth which can provoke phase shifting, in the exposed region of the quartz substrate 10.
A photosensitive film pattern 26 which exposes a portion of the light shield film pattern 20 adjacent to the groove 24 is formed on the light shield film pattern 20, in FIG. 5. The exposed portion of the light shield film pattern 20 is removed using the photosensitive film pattern 26 as an etch mask. The photosensitive film pattern 26 is removed. Consequently, a phase non-shift region 24a is set on the quartz substrate 10 at the circumference of the groove 24, in FIG. 6.
A method of fabricating the conventional rim-type halftone PSM shown in FIG. 2 will now be described.
As shown in FIG. 7, in the rim halftone PSM, as opposed to the general rim PSM, a phase shift layer 28 is additionally formed between a quartz substrate 10 and a light shield film 20. The light shield film 20 and the phase shift layer 28 are anisotropically etched using a photosensitive film pattern 30, which is formed on the light shield film 20 and exposes part of the light shield film 20, as an etch mask. Then, the photosensitive film pattern 30 is removed. As a result, as shown in FIG. 8, a predetermined region 32 of the quartz substrate 10 is exposed. This region is a phase non-shift region.
Referring to FIG. 9, a photosensitive film pattern 34 which exposes a portion of the light shield film 20 adjacent to the exposed region 32 on the quartz substrate 10 is formed on the light shield film 20. The exposed portion of the light shield film 20 is removed using the photosensitive film pattern 34 as an etch mask, thereby exposing the phase shift layer 28 below the exposed portion of the light shield film 20. An exposed region 36 of the phase shift layer 28 is a phase shift region. The photosensitive film pattern 34 is removed, thereby forming the halftone PSM comprised of the predetermined exposed region 32 on the quartz substrate 20 and the predetermined exposed region 36 on the phase shift layer 28 at the circumference of the exposed region 32, as shown in FIG. 10.
In the method of fabricating the conventional rim PSM or rim halftone PSM as described above, the position of a rim region is shifted, in association with a method of forming a light shield film pattern and a main pattern comprised of a phase shift region and a phase non-shift region and setting (forming) a rim region (or a rim pattern). Such a problem occurs because registration, orthogonality, and grid of exposure equipment are not completely consistent with each other. Also, accuracy of the size and position of the rim pattern to be formed between the main patterns of the PSM becomes more important with an increase in the integration of a semiconductor device.